1. Field of the Invention
The present invention relates to an electronic musical instrument providing a plurality of channels from which musical tones are produced.
2. Prior Art
The keyboard employed in the conventional electronic musical instrument can be classified into the following two types.
1 First type of keyboard: a simple on/off switch is provided for each of the keys, so that an on/off event of each key is detected. PA1 2 Second type of keyboard: a change-over-type switch is provided for each of the keys, wherein this switch consists of a movable contact, first and second fixed contacts. Herein, a time required for performing a switching operation in which the movable contact is moved from the first fixed contact to the second fixed contact is measured, so that an average operating velocity (or an average depressing velocity) of the key is computed on the basis of the result of the measurement.
In the second type of keyboard, a tone volume and/or a tone color for the musical tone is controlled on the basis of the computed average operating velocity of the key, for example.
In general, an electronic musical instrument recently developed provides a plurality of channels for the production of the musical tones. This electronic musical instrument is designed such that when detecting the key-depression events of the keys which are simultaneously depressed, plural musical tones can be simultaneously produced in a polyphonic sounding manner.
Some of the electronic musical instruments each providing the second type of keyboard are designed as described above so that plural musical tones can be simultaneously produced. In such electronic musical instrument, the musical note corresponding to a key newly depressed is assigned to one of the channels after computing the average operating velocity of the key. Therefore, it takes much time to produce the musical tone after depressing the key. Particularly, in the case of the electronic musical instrument having a limited number of channels, if all of the channels are occupied in producing the musical tones, one of the channels of which musical tone is attenuated and its tone volume is the smallest is selected, so that a musical note corresponding to a newly depressed key is assigned to the selected channel. This process is called a truncate process. Since the truncate process is required in the conventional electronic musical instrument, it takes more time to actually produce the musical tone after depressing the key.
In order to solve the above-mentioned problem, the present applicant has proposed a new electronic musical instrument, of which technical features are disclosed in Japanese Patent Laid-Open Publication No. 4-52693. This electronic musical instrument provides the aforementioned second type of keyboard, and it is designed such that a musical note corresponding to a newly depressed key is assigned to a predetermined one of the channels when detecting an event in which the movable contact comes in contact with the first fixed contact in the newly depressed key. Thus, it is possible to reduce a time lag which is occurred when the musical tone is actually produced after depressing the key.
Meanwhile, in the case of the string-striking type instrument such as the piano, when the key is depressed so that key is rotated down about a predetermined fulcrum point, the rotating motion of the key is transmitted toward a hammer by means of a string-striking mechanism, so that the hammer is rotated by the inertia, and consequently, a string-striking operation is achieved. Due to the above-mentioned structure of the instrument, if the performer slowly and slightly depresses the key, the hammer is not rotated sufficiently, so that the hammer is returned back to its original position without actually striking the string, resulting that the musical tone is not produced.
However, in the conventional electronic musical instruments described before, even if the performer makes every effort to slowly and slightly depress the key so that the musical tone will not be actually produced, the musical tone must be actually and eventually produced. More specifically, in the case of the electronic musical instrument providing the first type of keyboard, the switch equipped with the key must be turned on even if the performer slightly depresses the key, resulting that the musical tone must be actually produced. In the case of another electronic musical instrument providing the second type of keyboard, even if the performer slowly depresses the key, the time which is required for the movable contact of the change-over-type switch to move from the first fixed contact to the second fixed contact must be measured so that the average operating velocity of the key is computed on the basis of the result of the measurement, resulting that the musical tone must be actually produced by a small tone volume corresponding to the computed average operating velocity of the key.
Thus, the conventional electronic musical instrument suffers from a drawback in that even if the performer stops depressing the key in the middle of the key-depressing motion or the performer unintentionally touches a key adjacent to the key to be depressed by mistake, the musical tone which is not intentionally designated by the performer must be eventually produced.
Moreover, in the foregoing electronic musical instrument as disclosed in the foregoing Japanese patent laid-open publication, the musical tone which is not intentionally designated by the performer as described above must be automatically assigned to the predetermined one of the channels when detecting that the movable contact comes in contact with the first fixed contact. In this case, an assigning operation by which a new musical tone is assigned to one of the channels must be carried out against the will of the performer.